Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). The long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
A cell reselection procedure may be performed in the 3GPP LTE. The cell reselection procedure allows a user equipment (UE) to select a more suitable cell and camp on it. The UE shall attempt to detect, synchronize, and monitor intra-frequency, inter-frequency and inter-radio access technology (RAT) cells indicated by a serving cell. That is, when camped on a cell, the UE shall regularly search for a better cell according to a cell reselection criteria. If a better cell is found, that cell is selected. The change of cell may imply a change of RAT.
The 3GPP LTE can provide a multimedia broadcast/multicast service (MBMS) service. The MBMS is a service which simultaneously transmits data packets to multiple users. If a specific level of users exists in the same cell, the respective users can be allowed to share necessary resources so that the plurality of users can receive the same multimedia data, thereby increasing resource efficiency. In addition, a multimedia service can be used with a low cost from the perspective of users.
Generally, a UE in a radio resource control (RRC) idle state (RRC_IDLE) may perform an inter-frequency cell reselection procedure based on frequency priorities set by a network. If the UE wants to receive the MBMS service provided by the 3GPP LTE, the UE may perform the cell reselection procedure by setting a priority of a specific frequency providing the MBMS service to the highest priority by itself. When the UE which is interested in the MBMS service is released from the serving cell, the UE may be redirected to a frequency not providing the MBMS service even though the UE is interested with receiving the MBMS service.
A method for guaranteeing an MBMS service continuity for the UE which is interested in the MBMS service is required.